P0352 Code: Ignition Coil B Primary/Secondary Circuit

What the P0352 code means

The computer runs each ignition coil by cutting the primary current at the exact moment. While it does that, it monitors the circuit current to check that the coil is connected and responding.

The P0352 code says that monitoring gave an abnormal result on the coil identified as B. The letter follows the manufacturer order and almost always matches cylinder two, although you should confirm it in the vehicle documentation.

Like its sister code, it differs from a P0302 in that here the problem is declared as electrical. When both appear together, repairing the circuit usually solves both.

It is worth explaining why the computer can detect a coil problem before a misfire ever happens. The system does not only check whether there is current. It also measures the time the primary takes to charge up to the expected value. A coil with a degraded winding takes longer than it should, and that is detected before the spark actually fails.

That is why you can have a P0352 with an engine that seems to run well. It is an early warning, and dealing with it at that point avoids reaching a misfire and the catalytic converter damage that would come after.

P0352 code symptoms

• Check engine light on or flashing.
• Unstable idle and vibration.
• Lack of power and hesitation when you accelerate.
• Hard starting.
• High fuel use and a smell of unburned gas.
• The code is present with an engine that seems to run fine, as an early warning.
• Loss of power that only shows up in hard acceleration.
• The code shows up on rainy or very humid days and goes away in dry weather.

Likely causes of the P0352 code

1. Failed ignition coil B.
2. Connector with moisture, green corrosion or backed-out pins.
3. Control wire cut, rubbed through or shorted to ground.
4. Spark plug with an excessive gap or heavily worn.
5. Poor power supply to the ignition circuit.
6. System ground loose or rusted.
7. Damaged output driver in the computer.
8. Degraded primary winding, which takes longer than expected to charge without the spark failing yet.
9. Moisture inside the spark plug well after pressure washing the engine.
10. Hardened rubber seal on the coil, which lets water and dirt into the well.
11. Hairline crack in the plastic body of the coil, which only leaks to ground in high ambient humidity.

How to diagnose the P0352 code step by step

1. Swap the coil with another one on the engine, clear the code and read again. If the code changes letter, the coil is the culprit.
2. Measure the primary resistance and compare it with the specification.
3. Check for 12 volts of supply and continuity of the control wire.
4. Rule out a short to ground by measuring between the control wire and the chassis with the computer unplugged.
5. Check the connector and the harness for moisture and rubbing.
6. Examine the matching spark plug and its gap.
7. Look for water inside the spark plug well, especially if the code appeared after pressure washing the engine.
8. Check the condition of the rubber seal on the coil. Hardened or cracked, it lets moisture in and causes intermittent faults.
9. Read again after drying the well with compressed air, before you decide to replace anything.
10. Look at the coil body in dim light with the engine running. A visible leak that looks like a bluish spark confirms the crack.

How to fix the P0352 code

• Replace the coil when the swap test or the measurement points to it.
• Change the spark plugs as a set and gap them to the specification.
• Repair the wiring and replace the damaged connector.
• Clean and tighten the ignition system grounds.
• Check the circuit power supply and its fuse.
• Dry the spark plug well with compressed air and replace the rubber seal on the coil if it has hardened.
• Avoid pressure washing directly onto the coil area. It is the cause of many later faults.
• Replace the coil if the charge time is still out of range after ruling out moisture and the connector.
• Replace the coil if you can see a leak in dim light, even if its resistance readings are correct.

Technical reference data

• Typical primary resistance: 0.5 to 2 ohms. Secondary: 6,000 to 15,000 ohms.
• Acceptable voltage drop on the control wire: below 0.2 volts.
• Spark plug gap: 0.7 to 1.1 millimeters (about 0.028 to 0.043 in).
• Letter B is the second coil in the manufacturer order, normally cylinder two.
• Primary charge time in a healthy system: between 2 and 5 milliseconds depending on rpm.
• A longer charge time points to a degraded winding before the spark actually fails.
• A coil with a hairline crack can show correct resistance readings and still leak to ground in high humidity.

Brand-specific notes

If several coil codes appear at once (P0351, P0352 and the following ones), stop suspecting the individual coils and check the shared power supply, the ignition system fuse and the grounds. It is very unlikely that all of them fail at the same time.

Pressure washing the engine bay is a surprisingly common cause of coil codes. Water collects in the spark plug well, does not evaporate and causes leaks that show up days after the wash.

Frequently asked questions about P0352